1. Field of the Invention
This invention relates to an end cap assembly for a fluid resistant electrical device, wherein the assembly includes an insulating tube end cap and a grooved, cylindrical insert or plug which is securely positioned within a tubular opening of the end cap.
2. Description of the Prior Art
Fluid resistant electrical devices are widely utilized in various applications. As an example, oil immersible current limiting fuses are used in combination with expulsion fuses for protection of high voltage primary circuit components such as distribution transformers. The current limiting fuse has an element which is designed to rupture and interrupt the circuit upon the occurrence of a relatively high current, primary fault, while the expulsion fuse, in contrast, provides protection against lower amperage overload currents.
Expulsion fuses or switchgear are often immersed in insulating transformer oil and thus, in order to save space and eliminate the use of drywell canisters, it is preferable to also mount the series wired current limiting fuse within the same oil filled tank. Consequently, the fuse must be completely sealed to resist oil infiltration over the life of the fuse regardless of any stresses imposed upon the fuse body during installation or subsequent use.
One known type of current limiting fuse has an end cap assembly which includes a threaded bore for electrical coupling of the fusible element to the circuit to be protected. During installation, the bolt is inserted through a terminal lug coupled to a lead of the circuit, and the bolt is then threaded into the bore in the fuse end cap assembly and sufficiently tightened to reduce the possibility of loosening, since a loose connection in a high voltage circuit can lead to hazardous, violent arcing. As can be appreciated, an electrician might apply relatively large amounts of torque stress to the fuse end cap assembly in an effort to insure that such loosening of the lug bolt does not occur. Unfortunately, such stresses may break the seal of the fuse and thus the oil resistant sealing capability can be unknowingly destroyed.
Moreover, during manufacture of the fuse, it is desirable to insert a quantity of gas within the fuse tube before sealing of the same so that the gas can later serve as a leakage indicator during subsequent testing. Consequently, it is important to assemble and seal the fuse quickly after insertion of the gas to provide a valid leak test.
In the past, certain current limiting fuses have been provided with an end cap assembly having a fuse tube end cap with outwardly-extending walls defining a tubular opening. The assembly also includes a cylindrical insert with a circumscribing groove and a shoulder adjacent the groove, and the shoulder is engageable with the outward end of the end cap walls defining the tubular opening as the insert is positioned partially within the opening. A quantity of solder adheres to both the insert and the walls of the opening. However, such construction can provide only a limited resistance to torque stress during installation of the fuse.
A lightning arrestor is another example of an electrical device that should resist entry of fluids over its field life. The arrestor, when mounted in an outdoor environment, should be constructed to prevent entry of rainwater and thereby protect internal electrical subassemblies. Alternatively, an arrestor immersed in insulating oil should be provided with means for substantially precluding the entry of oil.
Accordingly, it would be a desirable advance in the art to provide an electrical device end cap assembly which permits simple and rapid assembly during manufacture, while providing a highly effective fluid resistant seal that retains its integrity even when a relatively high torque is applied to the end cap during installation.